[chrome.displaySource] Implement LPCM audio encoder.

extensions/renderer/api/display_source/wifi_display/wifi_display_audio_encoder.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/renderer/api/display_source/wifi_display/wifi_display_audio_encoder.h"
 
 #include "base/logging.h"
 
 namespace extensions {
 
 WiFiDisplayAudioEncoder::WiFiDisplayAudioEncoder(
     const wds::AudioCodec& audio_codec)
     : audio_codec_(audio_codec) {}
 
 WiFiDisplayAudioEncoder::~WiFiDisplayAudioEncoder() = default;
 
 void WiFiDisplayAudioEncoder::Create(
     const wds::AudioCodec& audio_codec,
     const AudioEncoderCallback& encoder_callback) {
+  // Create a format specific encoder.
+  switch (audio_codec.format) {
+    case wds::LPCM:
+      CreateLPCM(audio_codec, encoder_callback);
+      return;
+    default:
+      break;
+  }
+
   // Report failure.
   encoder_callback.Run(nullptr);
 }
 
 size_t WiFiDisplayAudioEncoder::GetAudioCodecMode() const {
   DCHECK_EQ(1u, audio_codec_.modes.count());
   for (size_t mode = 0u; mode < audio_codec_.modes.size(); ++mode) {
     if (audio_codec_.modes.test(mode))
       return mode;
   }
   NOTREACHED();
   return kInvalidCodecModeValue;
 }
 
 }  // namespace extensions